Bud-Eating by Bullfinches in Relation to the Natural Food-Supply

Abstract

In primaeval Europe, the bullfinch (Pyrrhula pyrrhula) was presumably a bird of deciduous forest, feeding for most of the year on the seeds of various trees and herbaceous plants, and on the buds of trees in spring. In modern England, while its main habitat is still deciduous woodland, it also occurs in smaller numbers in cultivated habitats, such as farmland, gardens, and orchards; it often nests in hedgerows and shrubberies. In such artificial habitats, the large buds of various fruit trees are preferred to those of native woodland trees, and in many fruit-growing areas, the bullfinch has become a serious pest. Broadly speaking, the buds of trees are of two types: the flower buds, which produce the blossom and eventually the fruit; and the leaf buds, which produce extension growth and leaves. Thus the loss of flower buds from a tree results in fewer blossoms, and potentially a reduction in the yield of fruit. In most fruit varieties, damaged buds are replaced the following year by the development of ancillary buds, but in certain plum and gooseberry varieties there is no regeneration of fruiting points, and damage is cumulative (Wright & Summers 1960). Severe damage to the leaf buds of a tree, though rare, may apparently affect its future cropping potential, as well as spoil the shape of the tree. The extent of damage to the buds of fruit trees varies enormously from year to year, and in extreme cases many acres of trees may be completely stripped of flower-buds. In the present paper, the extent of damage in different years is considered in relation to the populations and food-supply of the bullfinch in deciduous woodland, the natural habitat. Field work was carried out mainly in Marley, an area of 116 ac of scrubby deciduous woodland at Wytham, 3 miles west of Oxford. A detailed description of the area is given by Gibb (1950). The numbers of bullfinches and the available food-supply in Marley were assessed at monthly intervals each winter. In addition, the damage caused by bullfinches to fruit buds was investigated on the nearest fruit-farm, which lies about a mile and a quarter to the south-west of Marley. Observations on the food of bullfinches and measurements of the extent of damage to fruit buds were obtained in the winters of 1961-62, 1962-63, and 1963-64; but measurements of population size, and the decline in food-stocks through the winter were obtained only in the latter 2 years. The purpose of this paper is to discuss the bud-eating habits of bullfinches. For this it is necessary to refer to the fluctuations in numbers and the food-supply in woodland, but these aspects of the problem will be treated in detail in a subsequent publication; and the reader is referred to the latter for a detailed description of the methods used and results obtained. Throughout this paper, the term 'winter' is used to cover the period from October to April inclusive.